You ask an interesting question. Of course, there are commercial shells with rubber ball loads and such, but the components aren't generally available to the public. The old standard was to remove the shot from a factory load and replace it with rock salt; however, there's the corrosive aspect of using salt, the range was limited, and who has rock salt these days.

I've not heard of using a load of primers. But, my experience is limited to making regular and gag loads (like slipping a black powder confetti load into a buddy's shell bag). There's an anecdote about a trap shooter who was barred from competition. The story goes, he would put a spent primer in with the shot of his re-loads. The primer would be mistaken for a target chip and a missed clay scored as a hit.

The main worry in working with reduced shotgun loads is the potential for a wad unknowingly remaining in the barrel. The subsequent shot can be disastrous.

In our PC world, you should probably call them "less-lethal" over "non-lethal" loads.